I actually bougt mine off a guy on ebay for a very good price. It comes with brackets and clamps that let you put the mirror right on the roll bar. The mirror says it is for a polaris but the roll bars are the same exact size for the teryx.
Just search "Polaris RZR 4 panel mirror 570 800 S XP RAZOR WIDE REAR VIEW MIRROR 3" on ebay to find the guy. He also sells a five panel mirror and a single rear view mirror.
the 4 panel is $50 and the 5 panel is $42. The single mirror is $25.